Multi-speed potentiometer servo

ABSTRACT

Amu multi-speed digital servo system uses coarse and fine error signals. The coarse error signal is modified and the fine error signal which is provided by combining a command signal with a feedback signal from a digital, continuous potentiometer is limited. The modified and limited signals are mixed to provide desired servo operation.

United States Patent 1191 Cohen et a1. h 1

1451 July 31,1973

Van Ostrand 318/665 X MULTl-SPEED POTENTIOMETER SERVO 3,431,474 3/1969 2,861,233 11/1958 McKeown 318/665 [75] Inventors. RIchard L. Cohen, Old Bridge, 3,196,429 7H9 1 Gross at alm 318,665 x Robe" Taylor, Wayne, both of 3,254,283 5/1966 Hunt 318/665 x NJ. 2,938,174 5/1960 Bulleyment 318/684 X [73] Assignee: The Bendix Corporation, Teterboro,

Ni Primary Examiner-T. E. Lynch AttorneyAnthony F. Cuoco and Plante, Hafiz,- Smith [22] F1led: M111. 31, 1971 & Thompson [211 Appl. No.2 129,830 I [57] ABSTRACT 52 us. c1 318/592, 318/665, 318/684 mum-speed digital Servo system s war-Se and [51 1111.01. G05b 11/18 fine error Signals The some error Signal is modified [58] Field 61 Search 318/665, 684, 592-595 and the fine error Signal which is Pr y combining a command signal with a feedback signal from a 5 R f r it digital, continuous potentiometer is limited. The modi- UNITED, STATES PATENTS fied and limited signals are mixed to provide desired 3,051,881 8/1962 1 31111111 318/592 servo a 2,864,044 [2/1958 Pardee, Jr 318/6 65 X 5 Claims, 4 Drawing Figures r' (COARSE 32 1 6 I l V POT E A I; i0 '6 I FEED-BACK c "b 38 i ELEMENT 4B A AMR I 1 6 156 ii ,2, \5 .22 1 I D/A m Tm CONVERTER J l :45 14A I l I 42 I I I Elf/$535" 1 i I "a 1 w 1 DIGITAL I cor gr wous E l I f 1 i h I I l l .1

PATENIED 3.749.997

POT. FEEDBACK ELEMENT 4B A D/A CONVERTER CHOPPER CIRCUIT DIGITAL' CONTINUOUS PO FIG. 28

E INVENTORS E R/CHAAD L COHEN f ROBERT m map I BY 2 26 A frag/v5 y 1] MULTI-SPEED POTENTIOMETER' SERVO cRoss R FERENCE TO RELATED APPLICATIONS This invention uses a digital continous potentiometer feedback element such as described in copending U. S. Application Ser. No. 127,998, filed Mar. 25, 1971 'by Richard L. Cohen}Harold-'Moreines and Walter Parfomak, and assigned to The 'Bendix Corporation, assignee of the present invention and now 0.8. Pat. No. 3,662,246. I g

BACKGROUND OF THE INVENTION 1. Field of the Invention I This invention relates to multi-speed servo systems andparticularly to-servo systems using coarse and fine error signals. More gparticiilarly, this invention relates to servo systems of the type described wherein a digital, continuous potentiometer is used as a fine signal feedback transducer.

2. Description of the Prior Art Multi-speed digital servo systems utilizing coarse and fine error signals for driving aircraft instrumentation are considerably more accurate than their single speed counterparts, but require a continuous element for the fine signal feedback transducer. Until the present invention synchros or shaft encoders have been utilized for this purpose. However, with the advent of the digital continuous potentiometer such as described in the referenced copending U. 8 Pat. l I0.,3l,662, 246, a'potentiometer feedback element has become feasible and, moreover, offers several distinct advantages. For example, simple digital 'to'analo'g conversions may be made as contrasted to the formerly requiredand more costly digital to synchro conversions. Additionally,

there is no theoretical limit to the number of speeds that the system can have and only one digital interface with sample and hold analog memories is required as opposed to the more complicated digital transfer logic and hold registers which have heretofore been necessary. I

SUMMARY OF THE INVENTION This invention contemplates a servo system using coarse and fine error signals and including means for limiting the fine error signal, and which signal is provided by combining a command signal with a feedback signal from a continuous potentiometer. The coarse error signal is converted to a signal at a predetermined frequency which is blocked as long as it is below a predetermined level. When the level is exceeded a signal is provided at the predetermined frequency and at a level that will completely override the fine error signal so that the coarse signal will control until the fine signal is close enough to final value to assume control.

One object of this invention is to provide a multispeed servo system utilizing coarse and fine error signals, and wherein the fine error signal is provided by combining a feedback signal from a continuous potentiometer with a fine command signal.

Another object of this inventionis to provide a servo system of the type described wherein there is no theoretical limit to the number of servo speeds.

Another object of this invention is to provide a servo system of the type described wherein the coarse error signal overrides the fine error signal to control the sys- DESCRIPTION or THE DRAWINGS FIG. 1 is a combination block diagram-electrical schematic of a multi-speed servo system according to the invention. 7

FIG. 2A is a graphical representation of a coarse error signal modified according to the invention.

FIG. 2B is a graphical representation of a fine error signal limited according to the invention.

FIG. 3 is a graphical representation showing fine feedback signal (E,) and course feedback signalIE waveforms.

DESCRIPTION OF THE INVENTION A conventional type potentiometer type feedback element 6 provides a coarse servo feedback signal E, and

is connected to an emitter element 413 of a transistor 4.

Transistor 4 has a base element 4C connected through I tor 15 to a.c. signal 'source 10 for being driven by the signal therefrom. Transistor 14 has a collector element 14A which provides a return pathfor the driving signal.

A coarse error signal is provided at a An operational amplifier 16 has a non-inverting input terminal connected to collector 4A of transistor 4 and to collector 14A of transistor 14 through a grounded resistor 18 and a coupling capacitorZtl. An inverting input terminal of amplifier 16 is grounded through a resistor 22. 7 i

A feedback loop connected to an output terminal of amplifier 16 andto the inverting input terminal of I the amplifier includes aresistor 24 and a resistor 26 grounded through resistor 22. Diodes 28' and 30 are connected in parallel opposing relation intermediate resistors 24 and 26 and are connected to ground. Zener diodes 32 and 34 are connected in parallel opposing relationship to the output terminal of amplifier l6 and are grounded through a resistor 36.

The aforenoted circuitry provides a modified coarse error signal E at an output terminal 38. The modified coarse error signal has a wave form as shown in the graphical representation of FIG. 2A, the generationof which wave form will be hereinafter explained. v A digital continuous feedback potentiometer 40, which may be. of the type described in the aforenoted copending U. S. Pat. No. 3,662,246, provides a fine feedback'signal E Signal E may be of the typehaving a saw-tooth wave form which rises from zero to maxicombining point 'a fine command signal from a fine command signal means 41 to provide a fine error signal and the error signal is applied to a chopper circuit 42. Chopper circuit 42 converts the combined signal to an a.c. signal and amplifies and demodulates said signal, and accordingly may be a device such as described at page 359,

' Electronics for Scientists, Malmstedt et al., Benjamin,

Chopper circuit 42 is connected through a resistor 44 and diodes 46 and 48 connected in parallel opposing relation across the chopper circuit to provide at an output terminal 45 a limited fine error signal E, having a wave form as shown in the graphical representation of FIG. 2B, the generation of which wave form will be hereinafter described.

Output terminal 45 is connected to output terminal 38 through a resistor 50 and a resistor 51 and is connected through resistor 50 to an input terminal 52 of a servo amplifier designated generally by the numeral 54. Servo amplifier 54 includes an amplifier 56 having an input terminal connected to terminal 52 and another input terminal connected to ground through resistors 58 and 60. A capacitor 61 is connected across resistor 60 and ground. The servoamplifier amplifies the signal at terminal 52 in both voltage and power which provides a driving signal for driving a servo motor and in this respect the system is of the conventional type such as described at page 84 (FIG. 119), Synchros and Servomechanisms, Philco Corp., 1954. The servo loop is closed by a suitable mechanical connection 81 between servo motor 77 and course potentiometer feedback element 6 and by another suitable mechanical connection 85 between servo motor 77 and fine potentiometer 40. Mechanical connections 81 and 85 may be, for purposes of illustration, gear trains as is well known in the art.

An output terminal of amplifier 56 is connected to a base 62C of a transistor 62 and to a base 64C of atransistor 64. Transistor 62 has an emitter element 628 connected to an emitter element 643 of transistor 64. A collector element 62A of transistor 62 is connected to'a suitable source of positive direct current shown as a battery 66 and a collector element 64A of transistor 64 is connected to a suitable source of negative direct current shown as a battery 68. Emitter elements 628 and 64B are connected to ground through a capacitor 70 and a J resistor 72. The emitters are connected through a resistor 74 to a point 76 intermediate the other grounded terminal of amplifier 56 and resistor 58. A servo motor coil, 77 is connected in parallel with capacitor 70 and resistor 72.

OPERATION OF THE INVENTION The coarse and fine error signals-provided by combining coarse feedback signal E and fine feedback signal E, with the respective command signals are mixed as shown in FIG. 1 to obtain proper servo operation, The fine error signal is limited by the circuitry including resistor 44 and diodes 46 and 48 so that for an input signal E. the maximum level of the output signal E, is, for example i .5 volts as shown in FIG. 2B. The coarse error signal is converted by transistors 4 and 14 to, for example, a 400 HZ signal and this latter signal is modified by the circuitry including amplifier l6, diodes 28 and 30 and zener diodes 32 and 34 to provide a signal at point 38 which is either at zero or i 9 volts as shown in FIG. 2A. g

Amplifier l6 and its associatedcircuitry provides no output as long as the inputsignal thereto is less than for example, 10 millivolts. However, when the input signal (E;) is greater than 10 millivolts, the output signal (15,) will be a 9 volt, 400 HZ signal that will completely override any fine error signal. The result will be that the coarse error signal is the controlling signal until the fine error signal is close enough to a'final value to assume control. The operation of amplifier 16 will be better understood if it is considered that when E, is less than 10 millivolts the output of the amplifier will be less than the breakdown voltage of zener diodes 32 and 34 and E will be zero. When E, is greater than 10 millivolts,

the voltage across diodes 28 and 30 is clamped to thediode voltage thereby preventing normal feedback action. The gain of amplifier 16, therefore, will increase to its open loop value.

From the aforegoing description of the invention it will be seen that a new concept in multi-speed servo systems is provided. The principle feature of the invention is that it eliminates synchro error transducers or shaft encoders which add to the complexity and cost of the apparatus. The device of the invention; in'obviating the need for this circuitry, provides a simpler more economical system.- i P Although but a single embodiment 'of the invention has been illustrated and described in detail, 'it'i's' to be expressly understood that the invention ishot' limited thereto. Various changes may also be made in the de-' sign and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is: l. A multi-speed servo system comprising: means for providing a fine error signal;

means for providing a coarse error signal; means connected to the fine error signal means for limiting the signal therefrom; means connected to the coarse error signal means for modifying the signal therefrom to provide a signal which overrides the fine error signal so that-the 'coarse error signal is controlling until thefine error signal is close enough to final value to assume con trol, said means including means for converting the coarse error signal to a signal at a predetermined frequency and means responsive to said signal for providing a signal at said frequency and at a predetermined level when the signal from the converting means exceeds another predetermined level; and means for mixing the limited and modified signals to provide a driving signal.

2. A system as described by claim 1, whereinzthe means for mixing the limited andmodified signals to means for providing a coarse command signal; 4. A system as described by claim 3, wherein the first means for providing a coarse feedback signal; means includes: means for providing a fine command signal; a first current flow control device having an input elmeans for providing a fine feedback signal; ement connected to the coarse command signal means connected to the fine command signal means 5 means, a control element connected to a source of and to the fine feedback signal means and responenergizing voltage and an output element; and

sive to the signals therefrom for providing a fine a second current flow control device having an input error signal; 7 element connected to the coarse feedback signal means for limiting the fine error signal; means, a control element connected to the source .means connected to the coarse command signal 10 of energizing voltage and an output element conmeans and to the coarse feedback signal means and nected to the output element of the first current responsive to the signals therefrom for providing a flow control device. signal which overrides control by the fine error sig- 5. A system as described by claim 4, wherein the first naluntil said signal is close enough to final value to means includes:- assume control, said means including first means an operational amplifier having an inverting input responsive to the coarse command and feedback terminal, a non-inverting input terminal connected signals for providing a signal at a predetermined to the output elements of the first and second curfrequency and second means connected to the first rent flow control devices and an output terminal; means and responsive to the signal therefrom for a first pair of current flowv control devices connected providing a signal at said frequency and at a predein parallel opposing relation across the inverting termined level when the signal from the first means input terminal and the output terminal; and exceeds another predetermined level; and a second pair of current flow control. devices conmeans for mixing the limited signal and the signal nected in parallel opposing relation to the outputprovided by the last mentioned means to provide a tenninal. I a driving signal.

Inventor(s) UNITED STATES PATENT OFFICE CERTIFICATE ()F CORRECTIQN Patent No. 3,749,997

Dated July 31 19 73 RICHARD L. COHEN, ET. AL.

It .is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 1, "Amu m u1ti-speed" shou 1d read A mnlti-s peed Signed and sealed this 22nd day of January 1974.

(S Attest:

EDWARD M.PLETCHER,JR.

RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

1. A multi-speed servo system comprising: means for providing a fine error signal; means for providing a coarse error signal; means connected to the fine error signal means for limiting the signal therefrom; means connected to the coarse error signal means for modifying the signal therefrom to provide a signal which overrides the fine error signal so that the coarse error signal is controlling until the fine error signal is close enough to final value to assume control, said means including means for converting the coarse error signal to a signal at a predetermined frequency and means responsive to said signal for providing a signal at said frequency and at a predetermined level when the signal from the converting means exceeds another predetermined level; and means for mixing the limited and modified signals to provide a driving signal.
 2. A system as described by claim 1, wherein the means for mixing the limited and modified signals to provide a driving signal includes: means connected to the fine error signal limiting means and to the means responsive to the converted coarse error signal, and responsive to the limited fine error signal and the signal at the predetermined frequency and level for providing the driving signal.
 3. A multi-speed servo system, comprising: means for providing a coarse command signal; means for providing a coarse feedback signal; means for providing a fine command signal; means for providing a fine feedback signal; means connected to the fine command signal means and to the fine feedback signal means and responsive to the signals therefrom for providing a fine error signal; means for limiting the fine error signal; means connected to the coarse command signal means and to the coarse feedback signal means and responsive to the signals therefrom for providing a signal which overrides control by the fine error signal until said signal is close enough to final value to assume control, said means including first means responsive to the coarse command and feedback signals for providing a signal at a predetermined frequency and second means connected to the first means and responsive to the signal therefrom for providing a signal at said frequency and at a predetermined level when the signal from the first means exceeds another predetermined level; and means for mixing the limited signal and the signal provided by the last mentioned means to provide a driving signal.
 4. A system as described by claim 3, wherein the first means includes: a first current flow control device having an input element connected to the coarse command signal means, a control element connected to a source of energizing voltage and an output element; and a second current flow control device having an input element connected to the coarse feedback signal means, a control element connected to thE source of energizing voltage and an output element connected to the output element of the first current flow control device.
 5. A system as described by claim 4, wherein the first means includes: an operational amplifier having an inverting input terminal, a non-inverting input terminal connected to the output elements of the first and second current flow control devices and an output terminal; a first pair of current flow control devices connected in parallel opposing relation across the inverting input terminal and the output terminal; and a second pair of current flow control devices connected in parallel opposing relation to the output terminal. 